In many processes for the production of synthetic hydrocarbonaceous products, such as paraffins, alcohols and the like, it is necessary to produce a synthesis gas stream of carbon monoxide and hydrogen in proper proportions for reaction as a feed stream over a suitable catalyst. Fischer-Tropsch processes are well known and are frequently used for this purpose. The synthesis gas mixture may be produced by a number of processes, such as downhole gasification of coal or other hydrocarbonaceous materials, steam reforming of methane, partial gasification of hydrocarbonaceous materials, such as coal, at an earth surface and the like. In such processes, the carbon monoxide and hydrogen are frequently produced in combination with methane, acid gases, such as hydrogen sulfide, carbon dioxide and the like, as well possibly tars, particulates and the like. These materials are detrimental to the catalytic process for the conversion of the carbon monoxide and hydrogen into other products. Accordingly, a synthesis gas mixture is typically treated after production to remove tars, particulates and water as necessary by known technologies. Similarly, carbon dioxide and hydrogen sulfide are readily removed by known techniques, such as amine scrubbing and the like.
The production of LNG can be accomplished with a mixed refrigeration system, as well as other types of refrigeration systems such as cascade systems and the like. The mixed refrigeration systems shown in U.S. Pat. No. 4,033,735 issued Jul. 5, 1977 to Leonard K. Swenson (Swenson) and assigned to J. F. Pritchard and Company and U.S. Pat. No. 5,657,643 issued Aug. 19, 1997 to Brian C. Price (Price) and assigned to The Pritchard Corporation, are illustrative of mixed refrigerant processes for the liquefaction of natural gas. Both these references are hereby incorporated in their entirety by reference.
Normally the production of LNG, which is primarily liquefied methane, can be accomplished with a mixed refrigeration system such as those described above, but the presence of carbon monoxide and hydrogen in the stream require additional processing, since the carbon monoxide and hydrogen will not condense at LNG condensation temperatures. The primary separation step typically used is a synthesis gas fractionator, which requires an overhead temperature of nearly −177° C. In order to perform this separation, low temperature refrigerant is required for the fractionator condenser system. Nitrogen is a good choice for this system to provide this low temperature utility.
As a result, a continuing search has been directed to improved processes for the separation of carbon monoxide and hydrogen from methane economically.